Method of preparing colloidal sulphur



Ho Drawing.

Patented June 17, 1930 UNITED STATES PATENT OFFICE HENRY HOWARD, OF CLEVELAND, OfiIO,

ASSIGNOB, BY KESNE ASSIGNMENTS, TO'

THE GBASSELLI CHEMICAL COMPANY, OF CLEVELAND, 01110, A CORPORATION OF DELAWARE METHOD O l PREPARING COLLOIDAL SULPHUR Application filed November 17, 1926. Serial No. 148,999.

The present invention relates to a process fid (CaS),or as lime sulphur. Calcium sulfid for preparing colloidal sulphur from aqueous solutions of sulphur dioxide (sulphurous acid) and suitable compounds of calc um and sulphur.

Heretofore, colloidal sulphur has beenprepared by simultaneously passing hydrogen sulfid and sulphur dioxide into, water, these compounds then reacting according to the following equation:

been proposed to manufacture colloidal sulphur by acidulating lime sulphur solutions, but experimental data obtained on such processes indicates that while a finely divided sulphur may be thus obtained, it is not of the degree of fineness required for the true colloidal state.

The prinoigialobject of this invention is the provision o a process for preparin elemental sulphur which is in the true co oidal state, from compounds of calcium and sulphur, such ascalcium sulfid and lime sulphur, and sulphur dioxide. A further object of the invention is the provision of a process for preparin colloidal sulphur in which no evolution an escape of free hydrogen sulfid gas is likel to occur, and the resulting atmossuitable for use in my process may be prepared by roasting gypsum under reducing conditions, although calcium sulfid made in any other way-may, of course, be used. The

lime sulphur may be prepared in the usual wayby eating a mixture of milk of lime (a slurry of calcium hydroxide in water) and sulphur. The exact composition-of the resultipg lime-sulphur compound is not known with certainty, but it probably comprises a mixture of the persulfids Gas and 08s,.

In case calcium sulfid is used it is preferably added to the aqueous solution of sulphur dioxide in a finel divided solid condition and at a slow rate, t e essential condition being the maintenance of an excess of sulphur dioxide in the reaction mixture until the end point of the reaction is reached. The procedure may be carried out, for example, by a batch process in which the sulfid of calcium is run into an aqueous solution of sulphur dioxide which contains the total amount of sulphur dioxide needed to complete the reaction, or by a continuous process in which both the sulphur dioxide and sulfid of calcium are added either continuously or intermittently to the reaction mixture at such relative rates that an ex ss of sulphur dioxide is alwa s present. The course of the reaction is pro ably represented by the following equations:

(1 Gas +H SOa CaSO,+H; S g 2H S 'i' so, 3S (colloidal) 211 0 dal sul hur is applied, for example as a fulv lixci e. en lime sulphur is used instead of the calcium sulfid, the procedure is substantially the same, the lime sulphur being added in the form of an aqueous solution to the sulphur dioxide solution in controlled amounts so 100 osso,+sz=oas,o,+s (colloidal) j that an excess of sulphur dioxide there- 7 action mixture is maintained, and the final products are the same. A largler proportion of the available sulphur is, owever, converted into colloidal sulphur and therefore if the colloidal sulphur is the principal prodnot desired, the use of lime sulphur is more advantageous. The yield of. colloidal sulphur is increased by increasing the degree of saturation of the lime sulphur solution with sulphur, and for this reason the 11mg sul-' phur solution should preferably-contain the maximum amount of sulphur.

The maintenance of anexcess of sulphur dioxide in the reaction mixture is an essential feature of my process. It has been found that this condition results in an 'entirely diflerent set of reactions than. those which occur when sulphur dioxide is added to a reaction mixture containin ing the lime sulphuror calcium sulfi to an aqueous solution of sulphurdioxidein which the latter is present in excess, decomposition of the sulfid of calcium results and any hydrogen sulfid therebyformed reacts with the sulphur dioxide or sulphurous acid present to form colloidal sulphur, ,If the admixture ofthe sulphur dioxide and the sulfid of calcium .is effected by the reverseof this procedure, i. e., by treating sulfid of calcium with sulphur dioxide, the former being in excess, .any h drogen sulfid formed reacts with the sulfi of calciumto form calcium hydrosulfid ,(Ca (HS) After all" the sulfid of calcium has been converted into 'calcium hydrosulfid any further addition, of sulphur dioxide will cause the calcium hydrosulfid to decompose, liberating hydrogen sulfid which will escape from the reaction m1xture 1nto the atmosphere and be lost.

If desired the stability of the colloidal sulphur solut on ma be increased by adding a protective colloid to the aqueous solution of sul hur dioxide. Various colloids are suitab e for'this purpose, such as the waste,

liquor from the sulp ite pulp process. The

- protective colloid used must of course be one which is not decomposed by sulphurous acid. Protective colloids such as rosin soap are not w suitable for that reason.

an excess of lime sulphur or calcium sulfi "B add aqueous solution, the sul hur dioxide being maintained in. excess t roughout the reaction.

4. A rocess for preparing colloidal sulphur, w ich comprises reacting a sulfid of calcium with sulphur dioxide m aqueous solution and in the presence of a protective colloid, the sulphur dioxide being maintained in excess throughout the reaction.

5. A recess for preparing colloidal sulphur, which comprises reacting a sulfid of calciumwith sulphur. dioxide in aqueous solution, and in t e presence of the active constituents of sulfite cellulose waste h nor, the sul hur dioxide being maintain 1n excess t roughout the reaction. 6. Aprocess for preparing colloidal sulphur, which comprises reacting lime sulphur containin the maximum amount of sulphur with sulp ur dioxide in aqueous solution, the sul hur dioxide being maintained m excess t roughout the reaction.

In testimony whereof, I aflix m signature.

HENRY H WARD. 

